SHUTDOWN is accepted even if incoming user data is missing

[tuexen]

Why does the following script does not issue an ABORT in response to the SHUTDOWN?

// Create a blocking 1-to-1 style socket
+0.0 socket(..., SOCK_STREAM, IPPROTO_SCTP) = 3
+0.0 bind(3, ..., ...) = 0
+0.0 listen(3, 1) = 0
+0.0 < sctp: INIT[flgs=0, tag=1, a_rwnd=1500, os=1, is=1, tsn=1]
+0.0 > sctp: INIT_ACK[flgs=0, tag=2, a_rwnd=..., os=..., is=..., tsn=1, ...]
+0.1 < sctp: COOKIE_ECHO[flgs=0, len=..., val=...]
+0.0 > sctp: COOKIE_ACK[flgs=0]
+0.0 accept(3, ..., ...) = 4
+0.0 close(3) = 0

// Inject the first message and verify the immediate sending of a SACK
+0.0 < sctp: DATA[flgs=BE, len=116, tsn=1, sid=0, ssn=0, ppid=0]
+0.0 read(4, ..., 200) = 100
+0.0 > sctp: SACK[flgs=0, cum_tsn=1, a_rwnd=..., gaps=[], dups=[]]
// Inject the third message (the second is missing)
+0.0 < sctp: DATA[flgs=BE, len=116, tsn=3, sid=0, ssn=3, ppid=0]
// Check if a SACK with a gap report is sent immediately
+0.0 > sctp: SACK[flgs=0, cum_tsn=1, a_rwnd=..., gaps=[2:2], dups=[]]

// Tear down the association
+1.0 < sctp: SHUTDOWN[flgs=0, cum_tsn=0]
+0.0 > sctp: SHUTDOWN_ACK[flgs=0]
+0.0 < sctp: SHUTDOWN_COMPLETE[flgs=0]
+0.0 close(4) = 0